[FFmpeg-user] Video jumps after segmenting, transcoding, and rejoining video

[Dennis Mungai]

On Wed, 17 Jul 2019 at 11:41, Paul Cruickshank <cruickshankpg at gmail.com>
wrote:

> Hi,
>
> We're working on a project to have a highly parallelized video rescaling
> pipeline but we're finding that small audio and video jumps are being
> introduced into the video when we put the video back together. Can anyone
> point out anything we're doing wrong?
>
> The pipeline has 3 stages. First we split the video using the segment muxer
> $ ./ffmpeg -i samples/2160p-h264-aac-20mbs-2m.mp4 -muxdelay 0 -muxpreload 0
> -c copy -copyts -f segment -fflags
> +genpts -segment_time 4 -segment_format mpegts out/segments/%04d.ts
>
> Then we change the scale for each of the segments using:
> $ ./ffmpeg -i out/segments/0000.ts -muxdelay 0 -vf scale=1920:1080 -c:v
> libx264  -g 96 -keyint_min 96 -sc_threshold 0 -profile:v main -c:a aac
> -copyts out/segments/out00.ts
>
> And then we rejoin
> $ ./ffmpeg -i
> "concat:out/segments/out00.ts|out/segments/out01.ts|out/segments/out02.ts"
> -c copy -copyts out/transcoded.mp4
>
> The jumps seem to correlate to the segment boundaries. The jumps are even
> worse if we have to change audio codec from ac3 to aac in the middle
> transcode stage. It we skip the middle rescaling stage then we don't get
> any jumps in the output video so it's something that's going wrong in that
> command.
>
> For reference the commands are using ffmpeg 4.1.3 and the video I tested
> the commands with
>
> http://downloads.4ksamples.com/videos/PUPPIES%20BATH%20IN%204K%20(ULTRA%20HD)(Original_H.264-AAC)%20(4ksamples.com).mp4
>
> Thanks,
> Paul
>
>
See the changes above and retest


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